mmc: dw_mmc: Fix null dma_ops access when use_dma is false

host->dma_ops is not valid if host->usa dma is 0 so protect
host->dma_ops reference in dw_mci_resume

Signed-off-by: Jonathan Kliegman <kliegs@chromium.org>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Acked-by: Will Newton <will.newton@imgtec.com>
Signed-off-by: Chris Ball <cjb@laptop.org>